The invention is based on a method for signaling various header data.
In packet switched telecommunications networks, payload data are transmitted from a sender to a receiver in packet data units. The packet data units pass through a number of protocol layers in the sender before they are finally sent to the receiver via the telecommunications network. In the process, the individual protocol layers add header data in the form of so-called protocol control data to the actual payload data. These data are also referred to as “headers”. The header data with the protocol control data and the payload data then respectively comprise a packet data unit. In this connection, the protocol control data are used for example to convey the respective packet data unit with the payload data through the telecommunications network to the receiver. As a result, an on the whole relatively large quantity of data can be combined for the protocol control data, which also have to be transported along with the payload data. Particularly in systems with limited bandwidth, as is the case, for example, in mobile radio systems or in telecommunication connections via modems, this especially impedes the bit rate available for the transmission of the payload data.
Compression algorithms are used to reduce the data quantity of the protocol control data. These compression algorithms are known, for example, from the documents RFC 1144, Compressing TCP/IP Headers for Low-Speed Serial Links (D1), RFC 2507, IP Header Compression, M. Degermark, B. Nordgren, S. Pink (D2), and RFC 2508, Compressing IP/UDP/RTP Headers for Low-Speed Serial Links (D3). Reference D2 has disclosed a first group of compression and decompression algorithms of IP headers (Internet Protocol) in combination with TCP headers (Transport Control Protocol) and UDP headers (User Dataframe Protocol). Reference D3 has disclosed a second group of compression and decompression algorithms, which are based on the compression and decompression algorithms described in reference D2, but are only used for IP/UDP/RTP headers (RTP=Real Time Protocol). If packet data units are transmitted from a sender that contains a compressor, to a receiver that contains a decompressor, then the decompressor must be notified as to the nature or type of header data that it is currently receiving. This is usually assured through a corresponding signaling in the form of additional data, as described in the specification “Subnetwork Dependent Convergence Protocol (SNDCP)”, which are sent to the receiver along with the corresponding packet data unit. In this case, for some types of header data with different signaling, a first decompression algorithm is provided in the first group of algorithms and a second decompression algorithm is provided in the second group of algorithms, where the first decompression algorithm and the second decompression algorithm correspond to each other.